Silicate bonded foundry mold and core sands

ABSTRACT

MIXTURES OF A REFRACTORY MATERIAL WITH AN ALKALI METAL SILICATE AND HUMIC ACID PRODUCE A FOUNDRY SAND COMPOSITION FOR USE IN MAKING MOLDS AND CORES WHICH IS RE-USEABLE UPON BREAKING UP, RE-MILLING AND RE-WETTING THE USED MOLDS WHICH IS RE-USEABLE UPON RE-WETTING AND RMILLING DRIED OUT SAND. A UNIQUE FOUNDRY SAND BINDER COMPRISING A SOLID, WATER-SOLUBLE ALKALI METAL SILICATE AND HUMIC ACID ALSO DISCLOSED.

3,832,191 SILICATE BONDED FOUNDRY MOLD AND CORE SANDS Donald B Bolding and Hilton S. Williams, Houston, Tex., assignors to NL Industries, Inc., New York, NY. N Drawing. Filed Sept. 20, 1972, Ser. No. 290,721 Int. Cl. B28b 7/34 U.S. Cl. 10638.3 26 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field This invention relates to an improved foundry sand composition containing an alkali metal silicate binder. One aspect of this invention relates to a binder for foundry sand compositions. Another of the aspects of this invention relates to a method for the preparation of foundry sand compositions.

Prior Art Silicate bonded foundry sands are widely known. They have been used extensively in making molds and cores for the casting of steel, white and grey irons, nodular cast iron, copper and nickel base alloys, and alloys of aluminum and magnesium. Such foundry sands are composed of a major proportion of a suitable refractory sand, an alkali metal silicate binder, and other materials to improve certain properties of the foundry sand such as finely divided coal, clays, dextrose and the like. The silicate bond is obtained by precipitating silica gel from the alkali metal silicate by the addition of an acid or an acid producing gas such as carbon dioxide, or by dehydrating the alkali metal silicate such as by evaporation, heating, reaction and the like. Usually a combination of these two processes is used such as under-gassing with carbon dioxide, that is, using an amount of CO which is insufficient to precipitate all of the silica gel, and dehydrating the remainder of the silicate by evaporation.

An excellent book providing background in the field of silicate bonded foundry molds and cores is Foundry Core And Mould Making By The Carbon Dioxide Process, A. D. Sarkar, 1964, The Macmillan Co., 60 Fifth Avenue, New York, N.Y., Library of Congress Card No. 64-17167.

Although the carbon dioxide process is widely used and has certain advantages over other methods of producing molds and cores, this process has certain disadvantages which limit its usefulness. Thus silicate bonded molds cannot be broken up and the foundry sand re-used after castings have been made from them without extensive treatment. A marked deterioration in the strength properties of a silicate bonded sand occurs upon repeated re-use of the sand. Also where the alkali metal compounds around the sand grains are not removed, the build-up of low melting point alkali metal compounds in the sand mix upon addition of a silicate and re-use progressively reduces the refractoriness and increases the retained strength of the sand mix. For these reasons the foundry sand must be reclaimed using a wet scrubbing or pneumatic scrubbing process, if it is reclaimed at all, in

3,832,191 Patented Aug. 27, 1974 order to remove the old bond material, particularly the alkali metal compounds.

Silicate bonded foundry sands cannot be re-wet and re-worked upon drying. Contamination of clay-bonded sands and other sands used in the foundry with silicate bonded sands must be avoided as the surface finish deteriorates when pouring iron and steel castings in molds containing increased amounts of returned silicate bonded sands. Low SiO /Na O ratio silicates are undesirable since a large quantity of the sodium compound diminishes the refractoriness of the mold and core material, increases the retained strength, and prolongs the gassing time needed to neutralize the soda. High SiO /Na 0 ratio silicates develop poor strength upon gassing and are difficult to use because of their instability in the mill during mixing and their poor bench life. Molds and cores made from silicate bonded foundry sands have little or no green strength and must be gassed with CO heated or otherwise cured to enable the molds and cores to be used.

It is known to add water soluble salts of humic acid to clay bonded foundry sands. See for example U.S. Pat. No. 3,445,251. It is also known to add a mixture of humic acid and an aqueous emulsion of a high melting point asphaltic pitch to clay bonded foundry sands. See for example U.S. Pat. No. 3,023,113. Canadian Pat. NO. 843,443 discloses the use of alkali metal salts of humic acid as a temporary binder for granular or pulverulent materials, that is, a binder which is capable of being entirely or partially destroyed by a subsequent heating action.

It is also known that humic acid can be solubilized by reacting humic acid in an aqueous medium with basic materials, including sodium orthosilicate, Na SiO -5l-I O, and sodium metasilicate, Na SiO -5H O, as disclosed in U.S. Pat. No. 3,325,537.

SUMMARY OF THE INVENTION We have discovered a novel process for the precipitation of silica gel in foundry sand compositions containing alkali metal silicates to produce a silicate bond which eliminates many of the disadvantages of prior silicate bonded foundry sands. This process consists of reacting the alkali metal silicate with humic acid as hereinafter disclosed. The combination of an alkali metal silicate and humic acid produces a foundry sand which is re-useable upon breaking up used molds produced from the sand and re-milling them with the addition of a suitable amount of water and a small amount of additional bond material to replace that which is burned out during pouring of hot metal in the mold. This unique combination of bond materials also produces a silicate bonded foundry sand which can be re-wet and re-worked after drying, which does not adversely affect clay bonded sands used in the foundry, and which has good immediate green strength.

Accordingly it is an object of the present invention to prepare silicate bonded foundry sand compositions which are re-useable upon milling and re-wetting. It is another object of this invention to provide foundry sand compositions which can be re-wet and re-worked after drying. It is still another object of this invention to provide a method of producing such silicate bonded foundry sand compositions. A further object of this invention is to provide a unique foundry sand binder comprising a solid, watersoluble alkali metal silicate and humic acid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION These objects and other corollary objects and advantages of this invention are accomplished by preparing a foundry sand composition useful in the preparation of molds and cores which comprises a finely divided refractory sand, an alkali metal silicate, and humic acid. In

accordance with this invention it has been surprisingly found that a foundry sand composition containing an alkali metal silicate binder can be used repetitively if the alkali metal silicate is reacted with humic acid. A foundry sand containing sufiicient alkali metal silicate and humic acid has sufficient green strength that molds and cores prepared from the sand can be used immediately after their preparation, thus saving considerable time in this foundry operation.

Any typical refractory sand such as quartz sand, zircon sand, olivine sand or other refractory material may be employed in the practice of this invention. Such sands will have a fineness in accordance with the values proposed by the American Foundrymans Society (AFS) that. is in the range from about 25 to about 180. The characteristics of the sand used may in part be based on the type of metal being poured and the permeability desired in the finished mold or core. The method of determining the A FS foundry sand grade numbers and their significance is discussed in Foundry Core Practice by H. W. Dietert, AFS, 1952.

The alkali metal silicate, hereinafter sometimes referred to as silicate, useful in the practice of this invention may be any water-soluble alkali metal silicate, preferably a sodium silicate. Such silicates should have silica to alkali metal oxide molar ratios of at least 1:1, and preferably in the range from 2:1 to 4: 1. The silicates may be used in the foundry sand composition in either solution or solid form. The preferred silicate solution has a silica to alkali metal oxide mole ratio within the range from 2:1 to 4: 1, whereas the solid, water soluble silicate has a ratio within the range from 1:1 to 4:1, preferably 2:1 to 4: l. The preferred silicate solution contains from about 15% to about 55% by weight silicate. Water must be added to the foundry sand composition containing solid, water soluble silicate in order to solubilize at least a portion of the silicate. the amount of water used will generally be suflicient to provide from about 1.5% to about 6% water in the foundry sand composition upon initial mixing, preferably 2% to 6%. Water can also be added to a foundry sand composition containing silicate solution to provide from about 1.5% to about 6% water in the composition upon initial mixing, preferably 2% to 6%.

The humic acid useful in the practice of this invention is a material of wide distribution, being present in soils, peat and coals, especially coals of the type known as lignite, leonardite, or brown coal. Although the exact details of its chemical structure are not completely known, it is a surprisingly uniform substance considering the variety of source materials of which it represents a natural product of degradation, such as leaves, wood, and like vegetable organic matter. It is an acid, in which carboxyl and phenolic hydroxyl groups contribute base-combining ability. It is soluble in alkalies, has a deep brown color, and is readily soluble in water when coverted to its alkali metal salt.

For economic considerations the humic acid will generally not be extracted from its source material. Thus for purposes of this invention, the term humic acid is intended to designate any coal which meets the specifications for the class designated as Class IV, Lignitic, ASTM Designation D388-38, Classification of Goals by Rank, and any such coal can satisfactorily be employed as the source of humic acid. The richest common source of humic acid is lignite or leonardite, of which there are vast deposits distributed throughout the world, including the United States, and particularly the states of North Dakota, Texas, New Mexico, and California. Thus lignite or leonardite is the preferred source of humic acid.

We believe that the humic acid reacts with the solubilized silicate in the foundry sand composition to precipitate silica gel around the sand grains. The alkali metal salt of humic acid resulting from the reaction imparts initial green strength to the foundry sand which increases, as the free water is sorbed by the alkali metal humate or evaporates, to a point of dry strength and hot strength which is effected by the silica.

In the foundry sand composition of this invention the refractory sand is present in a major proportion of at least preferably at least by weight. The concentrations of silicate and humic acid are dependent upon several factors. Thus the concentration of silicate must be sufficient to provide the foundry sand with adequate hot strength such that molds or cores prepared from the sand will not deteriorate at the elevated temperatures encountered during the pouring of metals. The concentration of humic acid must be sufiicient to impart to the foundry sand sufiicient initial green compressive strength upon reaction with the silicate that good quality, easily handled molds and cores are obtained upon removing the pattern from the mold or the core from the core box. The compressive strength of the foundry sands of this invention increases with time and good quality, easily handled molds and cores can be prepared containing lesser amounts of silicate and humic acid if the molds and cores are allowed to age or are subjected to elevated temperatures before use.

In general the amount of alkali metal silicate used in preparing the compositions of this invention will be an amount to provide from about 0.5%5% by weight anhydrous alkali metal silicate in said compositions, preferably 0.65-4%, based on the total dry weight of the composition. The term anhydrous alkali metal silicate is intended to mean throughout the specification and claims the combined amount of silica and alkali metal oxide in the alkali metal silicate. The concentration of humic acid will generally be an amount to provide from about O.'3%5% by weight anhydrous humic acid in said compositions, preferably 0.3%-4%, based on the total dry weight of the composition. The term anhydrous humic acid is intended to mean throughout the specification and claims the humic acid remaining after removing water therefrom, such as by heating at C. overnight. That is, it is the humic acid on a moisture free basis.

The amount of humic acid is also dependent upon the amount of silicate in the foundry sand, the silica to alkali metal oxide mole ratio of the silicate, and the method of using the foundry sand to prepare molds and cores. An amount of humic acid greater than the amount required to neutralize all of the silicate may be used but is generally wasteful. Preferably the amount of humic acid will be less than the amount required to neutralize all of the silicate. In this manner the excess alkali metal silicate will set up producing a stronger mold or core than if all of the silicate is neutralized, hence, all of the silica gel precipitated. Generally, the weight ratio of anhydrous humic acid to anhydrous alkali metal silicate should be within the range from about 0.1:1 to 5:1, preferably 0.1:1 to 4:1.

Many methods of preparing foundry molds and cores from foundry mold and core compositions are known. Molds and cores can be prepared by placing the foundry sand composition in a mold box or a core box containing a pattern and ramming to achieve a uniform bulk density, thus producing a green mold or core having good strength and reproduction of pattern detail. After ramming, the mold box or core box is removed and the green mold or core used as is. Alternatively, the green mold or core can be stored before use or before removal from the box which will increase the compressive strength of the mold or-core. If desired, the mold or core can be heated to rapidly develop greater compressive strength either before or after removal from the mold or core box. The pattern within the mold box or core box can also be heated to effect a rapid strength development as in the production of shell molds.

Foundry sand compositions for preparing molds or cores by ramming procedures such as these contain an amount of silicate to provide from 0.5%-5% anhydrous alkali metal silicate, preferably 0.65%-4%, based on the total dry weight of the composition, an amount of humic acid to provide from 0.75 %-5% anhydrous humic acid, preferably 0.75%-4%, based on the total dry weight of the composition, from l.5%-6% water, preferably 2%- 6%, based on the total weight of the composition, and have a weight ratio of anhydrous humic acid to anhydrous alkali metal silicate within the range from 0.4: 1-521, more preferably 0.4: 1.4: 1. Such compositions should have an initial green compressive strength of at least 2 pounds per square inch (p.s.i.) When using a silicate solution as the source of alkali metal silicate, it is preferred that sufficient silicate solution is used to provide from 0.65% to 3% anhydrous silicate in the foundry sand composition of this invention. An amount of humic acid to provide from 0.75% to 4% anhydrous humic acid is preferred. The initial moisture content of the composition should be within the range from 1.5% to 4.5%, preferably 2% to 4.5%, while the anhydrous humic acid to anhydrous silicate ratio should be within the range from 0.8:1 to 5:1, preferably 0.8:1 to 4:1. When using a solid, water-soluble silicate as the source of alkali metal silicate, an amount is used to provide form 1% to 4% anhydrous silicate in the foundry sand. An amount of humic acid to provide from 1% to 4% anhydrous humic acid is preferred. The initial moisture content of the composition should be within the range from 2.5% to 6%, preferably 3% to 6%, while the anhydrous humic acid to anhydrous silicate mole ratio is within the range from 0.4:1 to 2.3: 1, more preferably 0.5 :1 to 2:1.

A special type of silicate bonded core composition is needed in those processes wherein the core composition is pneumatically blown or transported into the core box. These core boxes may be cold, at room temperature, or heated to several hundred degrees for rapid strength development. In normal foundry terms such processes are known as core-blowing, cold box, warm box, and hot box.

A difiiculty in pneumatically conveying silicate bonded foundry core sand compositions is due to the poor flowability of the compositions. Stickiness of such core compositions in the core box and on the underside of the blowplate in the core blowing machine also occurs preventing the production of good cores. Very few silicate bonded core sand compositions are useful for pneumatic conveying and they have a very short bench life; thus it is not possible to store the sand mix for a period of time before use.

These difiiculties can be overcome using as the foundry sand binder mixtures of alkali metal silicate and humic acid within certain specific concentration limits and weight ratios. Thus the foundry sand compositions for preparing molds or cores by procedures such as these contain an amount of silicate to provide from 0.5%- 2.75% anhydrous alkali metal silicate, preferably 0.65 2.5%, based on the total dry weight of the composition, an amount of humic acid to provide from 0.3%0.75% anhydrous humic acid, based on the total dry weight of the composition, from 2%-3.5% water, preferably 2%- 3%, based on the total weight of the composition, and have a weight ratio of anhydrous humic acid to anhydrous alkali metal silicate within the range from 0.111- 0.6: 1. Such foundry sand compositions should have an initial green compressive strength less than 2 p.s.i.

The foundry sand composition can be prepared in any conventional manner such as by admixing the refractory sand, silicate, and humic acid together in standard foundry mixing equipment until the desired green compressive strength is obtained. Water other than that provided by the silicate and the other ingredients can be added during mixing to provide an amount which is effective to impart the desired properties to the composition. The water will enable the silicate and the humic acid to react to' produce'the foundry sand compositions of this invention. It is preferable, though not necessary, to add the silicate and any necessary water to the refractory sand and mix these together before adding the humic acid. In this way the silicate is distributed around the sand grains before reaction with the humic acid. The water may be added to the silicate before addition to the refractory sand.

In a particularly preferred embodiment of this invention the foundry sand composition is prepared by admixing with a refractory sand a foundry sand binder comprising a mixture of a solid, water-soluble alkali metal silicate and humic acid. Water for solubilizing the silicate and effecting a reaction between the silicate and the humic acid is preferably added after first mixing the refractory sand with the foundry sand binder. The relative weight ratio of anhydrous humic acid to anhydrous silicate in the foundry sand binder is within the range from about 0.1:] to 2.321. The pH of a 5% by weight aqueous slurry of the foundry binder should be at least 9.0. The humic acid should contain less than 25% by weight moisture, preferably less than 20% moisture.

The foundry sand binder can be prepared by mixing together the humic acid and solid silicate in any suitable mixing or blending equipment such as double cone mixer, pug mill, ribbon blender, turbine mixer, or a tumbling barrel. Care should be taken to prevent undue moisture from entering the binder since the water may solubilize the silicate causing it to react with the humic acid. Generally the binder may contain up to about 30% water depending upon the amount of water of hydration of the silicate. The solid, water-soluble silicate can be mixed with dried, crude humic acid and the mixture pulverized to give the foundry sand binder of this invention.

The foundry sand composition of this invention can also contain additives to impart various characteristics to the molds and cores prepared from the composition. Thus finely divided silica flour, zircon fiour and the like can be added to decrease the surface friability of molds and cores. Such additives can be mixed with the humic acid and solid, water-soluble alkali metal silicate to produce a one-package product which needs only to be adequately mixed with sand and water to produce the foundry sand of this invention.

Molds prepared from the foundry sand compositions of this invention have been used successfully in preparing castings from aluminum, brass, cobalt (Stellite) alloys, iron and steel.

EXAMPLES The following examples will serve to further illustrate the invention. In these examples the source of humic acid is North Dakota leonardite which has been dried to 16% moisture and pulverized. It is sold by Baroid Division,

NL Industries, Inc. under the trademark Carbonox. The refractory sand used in these examples, unless otherwise indicated, is an AFS #64 fineness quartz sand obtained from Silica Products Co., Guion, Ark., under the designation #M-164. AFS #47 and AFS #88 quartz sands were used in some of the examples as indicated in Table III herinafter. The silicates used in these examples have the following characteristics:

g d g A Percent W91 ht base on the we! ht of FS #64 qualtz sand added water to give approximately the same concentration as was initially present in the composition. Again standard test specimens were prepared and tested as before. The data obtained are given in Table IV in the column designated Re-Used. Two molds were again prepared from each sand as before and brass at 2100 F. and aluminum at 1400 F. were poured into separate molds from each composition. The casting results are also given in Table IV.

These results indicate that foundry molds prepared from the foundry sand composition of this invention are re-useable without extensive treatment, in contrast with previously known silicate bonded sand compositions. This is is a decided economic advantage not only in those foundries which previously discarded their used silicate bonded molding sands, but also in those foundries which re-claim their used sand, because of the savings in time, labor, equipment and bond material.

This example illustrates a preferred foundry sand composition for use in preparing foundry cores or molds by a process involving pneumatic conveying of the composition. 100 lb. of #M-164 quartz sand, 2.0 lb. of Silicate D, and 0.67 lb. of humic acid were mixed in a conventional foundry muller for three minutes. Then 3.0 lb. of water was added and the mulling continued for four minutes. This foundry sand composition had a green compressive strength less than 2 p.s.i. Nine pounds of this foundry sand composition was loaded into a Pattern Work shell core blow machine which contained a steel corebox having three cavities. The corebox had been heated with a gas flame. The sand was blown into the hot corebox and retained for a short time. The corebox was then opened and the hot, solid finished cores removed. The cores may be relatively wet in their center, depending upon their retention time in the hot corebox, but the 3:-

surface of the cores are hard and dry and they can be easily handled.

Nine pounds of this same foundry sand composition was used in the same machine to make cores except that the corebox was not heated. In this case the cores were TABLE IV Example 51 Example 52 Foundry sand Foundry sand composltioncomposition- 3% 1 Silicate A 6% 1 Silicate A (1.05 Silicate A), (2.03% 2 Silicate A), 2% I humic acid 4% 1 humic acid 113% i h e (3.16% 1 humic acid) acid) Initial Reused Initial Re-used Percent water 3 3. 4 3. 5 3. 3 3. 4 Green compressive strengt 9.0 8. 6 10. 5 9. 5 Green shear strength 4. 3 5. 1 5. 2 4. 6 Permeability number.-." 123 130 97 116 Dry compressive strength:

24 hour air dry 55 86 2 hour oven dry at 250 F. 91 Hot strength at 1.000" F 93 90 102 97 Brass casting results:

Shake-out Good Good Good Good Good Good Aluminum casting results.

Shake-out Good Good Good Finish Good Good Good 1 Percent by weight based on the weight of AFS #64 foundry sand.

2 Percent by weight of anhydrous sodium silicate or anhydrous humic acid based on the total dry composition.

3 Percent by weight based on the total composition.-

4 Above average.

In the claims which follow the following apply: percent alkali metal silicate is intended to mean the concentration of alkali metal silicate on a 100% active, moisture free basis and is expressed as percent by weight of the total dry composition; percent humic acid is intended to mean the concentration of humic acid on a 100% active, moisture free basis and is expressed as percent by weight of the total dry composition; and, weight ratio of humic acid to alkali metal silicate is intended to mean the ratio of the concentrations as expressed in this paragraph, that is, the weight ratio of anhydrous humic acid to anhydrous alkali metal silicate.

We claim:

1. A foundry sand composition comprising a major proportion of refractory sand, an alkali metal silicate in an TABLE III Binder composition P.s.i.

Foundry sand composition Percent Green Air dry Ratio Percent comprescompres- Sili- Humic AHA/ sive slve cate Silicate arid AS 11 I Binder Water Sand strength strength 0 42.8 57.2 1. 37 3.5 3.5 AFS #64 3.6 40 C 42.8 57.2 1.37 3.5 4. 2 AFS #64 6.5 34 D 57. 2 42.8 0.77 3.5 3.5 AFS #64 3.2 70 D 60 40 0.68 5.0 3.8 AFS #64 2.3 280+ D 66 34 0. 53 5. 0 3. 6 .AFS #64 4. 9 280+ F 50 50 1. 02 4.0 3. 1 AFS #64 3.0 30 D 60 40 0.68 3.5 3.0 AFS #47 3.4 280+ D 60 40 0.68 3.5 3.0 AFS #88 3.6 280+ D 60 40 0.68 5.0 3.5 .AFS #88 3.4 180 D 58.3 41. 7 0.73 6.0 3. 6 8.8 205 D 60 40 0.68 5.0 3. 5 8.2 93 D 66 34 0.53 5. 0 3. 5 6. 2 D 62. 5 37.5 0.61 4.0 3. 6 3.5 103 D 07. 5 32. 5 0. 49 4. 0 3. 5 3.9 111 C 50 50 1.02 4 3. 6 5.2 48 O 428 57. 2 1. 37 3. 5 3. 2 6. 8 C 42.8 57. 2 1.37 3.5 3. 6 2.7 44 C 42. 8 57. 2 1. 37 5. 25 3. 6 11. 9 41 C 33. 3 66. 7 2. 05 4. 5 3. 6 6. 1 27 l AHA=anhydrous humic acid. 1 AS=auhydrous alkali metal silicate.

I n AHA/ n (peceit humic acid) (100% moisture) (percent silicate) (percent silica plus percent alkali metal oxide) amount to provide from 0.5% to alkali metal silicate in said composition, humic acid in an amunt to provide from 0.3% to 5% humic acid in said composition, and 1.5% to 6% by weight water, wherein the weight ratio of humic acid to alkali metal silicate is within the range from 0.1:1 to 5:1, and wherein the source of said humic acid is coal which meets the specifications for the class designated as Class IV, Lignitic, ASTM Designation D 388-3 8, Classification of Coals by Rank.

2. A composition in accordance with Claim ll wherein said alkali metal silicate is sodium silicate.

3. A composition in accordance with Claim 2 wherein said sodium silicate has a SiO :Na O mole ratio from 1:1 to 4: 1.

4. A composition in accordance with Claim 3 containing 0.65% to 4% sodium silicate, 0.3% to 4% humic acid, and 2% to 6% water, wherein said weight ratio of humic acid to sodium silicate is within the range from 0.1:1 to 4:1.

5. A composition in accordance with Claim 3 containing 0.65% to 3% sodium silicate, 0.75% to 4% humic acid, and 2% to 4.5% water, wherein said weight ratio of humic acid to sodium silicate is within the range from 0.8:1 to 4:1 and wherein said sodium silicate is obtained from a solution containing from about 15% to about 55% by weight sodium silicate.

6. A composition in accordance with Claim 5 wherein said sodium silicate has a SiO :Na O mole ratio within the range from 2:1 to 4: 1.

7. A composition in accordance with Claim 3 containing 1% to 4% sodium silicate, 1% to 4% humic acid, and 3% to 6% water, wherein said weight ratio of humic acid to sodium silicate is within the range from 0.4:1 to 23:1, and wherein said sodium silicate is obtained from a solid, water soluble sodium silicate.

8. A composition in accordance with Claim 7 wherein said sodium silicate has a SiO :Na O mole ratio within the range from 2:1 to 4: 1.

9. A composition in accordance with Claim 3 containing 0.65% to 2.75% sodium silicate, 0.3% to 0.75% humic acid, and 2% to 3.5 water, wherein said weight ratio of humic to sodium silicate is within the range from 0.1:1 to 0.6:1.

10. A composition in accordance with Claim 9 wherein said sodium silicate has a SiO :Na O mole ratio within the range from 2:1 to 4:1.

11. A foundry core composition comprising a major proportion of refractory sand, an alkali metal silicate having a silica to alkali metal oxide mole ratio from 1:1 to 4:1 in an amount to provide from 0.5% to 5% alkali metal silicate in said composition, and humic acid in an amount to provide form 0.3% to 5% humic acid in said composition, wherein the weight ratio of humic acid to alkali metal silicate is within the range from 0.1:1 to 5: 1, and wherein the source of said humic acid is a coal which meets the specifications for the class designated. as Class IV, Lignitic, ASTM Designation D 388-38, Classification of Coals by Rank.

12. A foundry sand binder composition comprising a solid, water soluble alkali metal silicate and humic acid in a weight ratio of humic acid to alkali metal silicate within the range from 0.1:1 to 2.3:1 such that a 5% by weight slurry of said binder has a pH of at least 9.0, wherein the source of said humic acid is a coal which meets the specification for the class designated as Class IV, Lignitic, ASTM Designation D 388-38, Classification of Coals by Rank.

13. A binder in accordance with Claim 12 wherein said alkali metal silicate is sodium silicate.

14. A binder in accordance with Claim 13 wherein said sodium silicate has a sio,:Na,o mole ratio within the range from 1:1 to 4:1.

15. A binder in accordance with Claim 14 wherein said sodium silicate has a siO zNa O mole ratio within the range from about 2:1 to 4:1.

16. A binder in accordance with Claim 15 wherein said weight ratio of humic acid to alkali metal silicate is within the range from 0.1 :1 to 0.6: 1.

17. A binder in accordance with Claim 15 wherein said weight ratio of humic acid to alkali metal silicate is within the range from 0.4:1 to 23:1.

18. A method of producing a foundry sand composition comprising:

adding to a refractory sand sufiicient alkali metal silicate to provide from 0.5% to 5% alkali metal silicate in said foundry sand, sufiicient humic acid to provide from 0.3% to 5% humic acid in said foundry sand, wherein the source of said humic acid is a coal which meets the specifications for the class designated as Class IV, Lignitic, ASTM Designation D 388-38, Classification of Coals by Rank, and sufficient water to provide from 1:5% to 6% by weight water in said foundry sand, provided that the weight ratio of humic acid to alkali metal silicate is within the range of from 0.1:1 to 5:1, and

mixing said foundry sand until the desired green comprehensive strength is obtained.

19. A method in accorance with Claim 18 wherein said green compressive strength is at least 2 p.s.i.

20. A method in accordance with Claim 19 wherein said alkali metal silicate is sodium silicate.

21. A method in accordance with Claim 20 wherein the siO zNa O mole ratio of said sodium silicate is within the range from 1:1 to 4: 1.

22. A method in accordance with Claim 20 wherein the mole ratio of said sodium silicate is within the range from 2:1 to 4:1.

23. A method in accordance with Claim 22 wherein the concentration of sodium silicate is 0.65% to 4%, the concentration of humic acid is 0.75% to 4%, the concentration of water is 2% to 6%, and said weight ratio of humic acid to sodium silicate is from 0.4:1 to 5: 1.

24. A method in accordance with Claim 22 wherein the concentration of sodium silicate is 0.65% to 3%, the concentration of humic acid is 0.75% to 4%, the concentration of water is 2% to 4.5%, and said weight ratio of humic acid to sodium silicate is from 0.8:1 to 5:1, wherein said sodium silicate is added in the form of a solution containing from about 15% to about 55% sodium silicate.

25. A method in accordance with Claim 22 wherein the concentration of sodium silicate is 1% t0 4%, the concentration of humic acid is 1% to 4%, the concentration of water is 3% to 6%, and said weight ratio of humic acid to sodium silicate is from 0.4:1 to 2311, wherein said sodium silicate is added in the form of a water soluble solid.

26. A method in accordance with Claim 18 wherein said alkali metal silicate is sodium silicate having a SiO :Na O mole ratio within the range from 2:1 to 4:1 and wherein the concentration of sodium silicate is 0.65% to 2.75%, the concentration of humic acid is 0.3% to 0.75%, the concentration of water is 2% to 3.5% based on the total weight of the composition, and said weight ratio of humic acid to sodium silicate is from 0.121 to 0.6: 1, and wherein said desired green compressive strength is initially less than 2 p.s.i.

References Cited UNITED STATES PATENTS 2,905,563 9/1959 Ilenda et a1. 106-38.35 3,285,756 11/1966 Moren 106--38.35 3,445,251 5/1969 Nevins 10638.35 2,975,494 3/1961 Cooper 106-3835 LORENZO B. HAYES, Primary Examiner US Cl. X.R. 

